The present invention relates to a wide angle photographic lens, particularly to an inverted-telephoto or retrofocus photographic lens.
It is well known that the retrofocus lens was developed to provide a long back focus to small focal length lenses. In such lenses compensation of aberrations is difficult because of the asymmetrical arrangement of the divergent lens group at the object end of the convergent lens group. Correction of distortion, curvature of field and halo of the off-axial sagital rays is particularly difficult. The smaller the length of the lens, the more difficult is the compensation.
In a conventional retrofocus type lens, the number of the lenses is increased to overcome the difficulty of correcting aberrations. This, however, is undesirable because it raises manufacturing costs.
The inventors of the present invention have described retrofocus type lenses consisting of a small number of lenses German Patent Publications 1062028 and 1187393. An investigation has been made to decrease the total lens length to improve the aberrations and increase the picture angle and the back focus of a photographing lens, mentioned in the German Patent Publication 1187393, whose F-number is 1:2.8, picture angle 2.omega. is 62.degree., back focus is 1.053f and lens length (the distance between the first surface and the last surface) is 1.274f.